Synthesis of poly(ε-caprolactone) by an immobilized lipase coated with ionic liquids in a solvent-free condition

Abstract

Polycaprolactone (PCL) was synthesized by ring-opening polymerization of ε-caprolactone through two different enzymatic processes. The lipase from Candida antarctica B, immobilized on macroporous acrylic acid beads, was employed either untreated or coated with small amounts of ionic liquids (ILs). Monocationic ionic liquids, [C(n)MIm][NTf2] (n = 2, 6, 12), as well as a dicationic ionic liquid, ([C4(C6Im)2][NTf2]2), were used to coat the immobilized lipase and also as the reaction medium. In both methods, the polarity, anion of the ILs concentration and viscosity strongly influenced the reaction. Coating the immobilized enzyme with ILs improved catalytic activity and less ILs was required to produce PCL with a higher molecular weight and reaction yield. At 60 °C and ILs/Novozyme-435 coating ratio of 3:1 (w/w) for 48 h, the highest M(w) and reaction yield of PCL were 35,600 g/mol and 62% in the case of [C12MIm][NTf2], while the M(w) and reaction yield of PCL was 20,300 g/mol and 54 % with [C12MIm][NTf2] and catalyzed by untreated lipase.